Koji KAMIYA,* Takayuki MIYAMAE, Makoto OKU**, Kazuhiko SEKI,** Hiroo INOKUCHI, Chizuko TANAKA*** and Jiro TANAKA*** (*Chiba Univ., **Nagoya Univ., ***Kanagawa Univ.)
[J. Phys. Chem. 100, 16213 (1996)]
The UPS spectra of cis- and trans-polyacetylene were measured by careful treatment of fresh samples. This is the first UPS measurement of cis-polyacetylene (cis-transiod). Assignments of the observed spectra are given by comparing with energy levels of cis- and trans-C20H20 obtained by ab initio MO calculation. The change of UPS spectra upon stepwise perchlorate doping was measured; at first the intensity of C2p(pi) band decreased and the whole band shifted to higher binding energy. By further doping, a new C2p(pi) band appeared close to the Fermi level EF when the conductivity reached 11000 S/cm. These change show insulator to metal transition accompanied with structural transformation. The UPS spectrum near EF showed a strong correlational effect characteristic of a low-dimensional conductor. The spectra of heavily perchlorate-doped and potassium-doped polyacetylene near EF are analyzed by a theory of Kopietz, Moden and Schönhammer (Phys. Rev. Lett. 74, 2997 (1995)).